Interpretive Summary: Production of ethanol from corn creates a byproduct, distillers' dried grains that must be sold to make the ethanol plants commercially viable. The byproduct is sold as animal feed and its price will be close to that of corn, usually around $0.05/lb. About half the protein in corn forms films readily and is insoluble in water. This alcohol extractable protein is called zein. There is a small commercial market (only a few tons/year) for pure zein at prices starting at $14/lb. This zein is extracted from a corn milling material which is about 60% protein. Less pure zein/corn oil mixtures (zein isolates) can be extracted directly from corn. Sale of zein isolate as a byproduct, in place of some of the distillers' dry grains should significantly reduce the overall cost of producing ethanol and enable U.S. corn producers to obtain and maintain higher return from the non-starch corn components. These components may be available in increasing amounts as more corn starch is converted to ethanol. Commercialization of zein isolation facilities attached to dry grind ethanol plants depends on demonstrating the key process steps and demonstration requires capital investment within the financial reach of prospective pioneers. We have previously shown that extracted corn can be separated from the liquid extract with inexpensive equipment. This article shows that settling zein extracts in a pilot scale tank is more effective than the smaller settling tank previously used and corroborates our earlier cost estimate of $1/lb of zein isolate.

Technical Abstract:
A pilot-scale settling tank was used to separate maize particles from extracts into water with little dilution of the aqueous ethanol extract liquid. The larger particles that settled in the first quarter of the tank were carried out by continuous water flow 76 cm below the extract layer. The large particles had an 80% higher protein mass fraction than the smaller particles that collected in the bottom of the settling tank downstream from the extract inlet. By confining the water flow to the bottom of the tank extracted particles were prevented from accumulating in the settling tank with a much lower water/extract flow rate ratio than needed for a smaller settling tank. The mass ratio of entrained extract liquid/settled solids (0.5) was half that observed in earlier settling runs with a smaller tank, probably as a result of the more stable extract/water interface. The finer meal, 1 mm screen size, did not improve the extraction of zein but did increase extract liquid entrainment compared to the usual 2 mm screen size. Consequently the 2 mm size is the minimum that should be used with this process.